/// https://leetcode.com/problems/convert-sorted-array-to-binary-search-tree/
/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    
    TreeNode* helper(vector<int> arr, int s, int e){
        if(s > e){
            return NULL;
        }
        
        int mid = (s+e)/2;
        int rootData = arr[mid];
        TreeNode* root = new TreeNode(rootData);
        root->left = helper(arr, s , mid-1);
        root->right = helper(arr, mid+1 , e);
        
        return root;
    }
    
    TreeNode* sortedArrayToBST(vector<int>& nums) {
        int n = nums.size();
        return helper(nums, 0 , n-1);
    }
};